Process of cracking mineral oil



May 23, `1933. A. E. PEw, JR

PROCESS OF CRACKING MINERAL OIL Filed Nov. 9, 1929 rf/arf )ogm BY Patente-d May- 23, 1933 UNITED STATES ARTHUR E. :PEw, am., or BRYN MAwIa.,

coMPANIL'or PHILADELPHIA, PENNSYLVANIA, A coRroRATIoN or NEW JERSEY PATENT OFFICE PCENNSYL'VANI, ASSIGNOR SUN' OIL PROCESS 'OF CRACKING MINERAL OIL 'Applicationled November In order to crack, in the vapor phase, crude oil or any product, such as gasoil, resulting from the distillation of crude oil, in order to produce comparatively low boiling products such as gasoline, such oil as is passed through the l"vapor phase cracking zone should not only be completely vaporized, but it is. important that the vapor should be perfectly dry. An oil'may be so completely vaporized that no entrained liquid may be separated therefrom by any mechanical device for throwing out any entrainediliquid, but it may still contain suiiiciently very inely divided particles or very moist' vapors that are practically'at'the dew point, in consequence of which, when the vapors are exposed to moderately lhigh temperatures, thereis a decided formation of carbon on the metal surface through which the heat is conducted to the vapors. The amount of carbon so formed is relatively very small, but it builds up on the -metal walls and in time so reduces or obstructs the flow that it is necessary to shut downthe equipment for cleaning. v

It is, of course, obvious that one-method of `overcoming this difculty is to superheat or raise the temperature of the va ors so that they are'completely dried and ree of any moisture or inely divided .ent-rainment. This method has been used for this purpose with proper 'distribution' ofheating surface. In

, a' very" mild form of heating this can be done with a reasonable degree of success. When,

however, the drying ofthe vapors .is efected in this way, the lack of uniform conditions,

which it is almost impossible to maintain,

m'ilitates against success. Any excessive temperature 1n the drying zone causes accumulation of Carbon in a relatively short period,'whi1e any drop in temperature inthe drying zone which does not fully dry the vapors, `even for relatively short periods, allows the moist vapors to go into the cracking 'zone' and thus form carbon very rapidly in the cracking tubes. Another cause of trou- 4ble with such an arrangement is tha'tvthe carrying over of any actual liquid into the'.

-drying zone causes the formation of vapors in the drying zone, which then are saturated or even carr entrained li uid thus introducv Y a s, 1929. serial No. 405,871.

ingsuch saturated vapor orentrained liquid.

into the .cracking tubes.

,The process involving the present inveneo cracking of the oil under a much reduced v' pressure which need not exceed the back pressure of the cracking and fractionating equipment.

The entire process will rst ,be described and the invention will then be particularly pointed out in the claims. The single figure of the drawing is a diagrammatic illustration of the a paratus which may be used.

The c arging stock, preferably gasoil, is

taken from the tank through line 1 and pump 2 -through heat exchangers 3 and 150 into the pipe still 4, where it is heated up to practically completely vaporize the oil as it enters the vaporizer 5. The. pump maintains in the vaporlzer line a substantial pressure, v say from 100-300 pounds. The vapors leave the top of vaporizer 5 and pass through aseparator 6', which -takes out any mechanical entrainment of liquid and preventsany liquid passing beyond thisV part of the line. Be-

ond separator 6 is a pressure-reducing valve. I ,which e-fects'or allows a drop of 50 or' more pounds of pressure, thereduced pressure not being necessarily higher (40 to 50 pounds) than the back pressure of the cracking and fractionating' equipment. The 'vapor then passes through line 8 intothe'vapor phase cracking coil 9, is raised therein to the required or. desired temperature (say about 950"A F.A or above) and passes out at 10 into the spray cooler toweri11, where it is cooled and partially separated. tower 11 the heavier portion is drawnv off at the bottom ,through outlet 12 and the remainder goes out as vapor through line 13 and into fractionating tower 16, where the lighter portions are separated. Gasoline and gas go out through line 17, through a clay tower23 `and through a condenser 24. into a gas separator 30. from which gasoline is taken out through line 31. The gas escapes through line 32 into an absorption tower 33 and the stripped gas 1s passed out throughline 34 to a gas holder or to theh atmosphere.

From tower 16 an intermediate product `is taken out through line 19 and, after passing the heat exchanger 3 and/or other coolers,

, goes to storage; or itmay be used again in the process by being conducted through by-pass line 190 to the feed or charging stock line; the product being very similar to the original gas oil which is used as charging stock.

All of the gasoline vapors and gas are not taken out oftower 16 through line 17, but a regulable proportion `is taken out through l line 18 and passes through condenser 26 into tank 27; the condensate being taken 'through pump 28 and line 22 back 'into the top of the fractionating tower. This condensate is .used

,for controlling the temperature at the top of the tower in order;l to tix the maximum boiling, point off the producttaken through line 17. Line 29 is the vent which vents thegas from tank 27 so'as to maintain the proper level of leads from the outlet at'the bottom of -vapor- Y 'izer 5, is for conveying away anyheavy ends such as a topped crude,

which may not be completely vaporized when the oil leaves thepipe still. This high boiling product may be carried'back into line `15, as shown, or may be withdrawn from the system. .If a relatively heavy charging stockg is used, then a considerable portion is drawn olf at the bottom of vaporizer 5 and this should then be passed y through line 14 into tower 11. Such heavy portions are exposed tothe highest temperporize any ature in tower 11 and in this way cracked to some extent and the heavy portions are drawn oil through line 12 along with the heavy products from the vapor phase cracking coil.

Due to the substantial pressure maintained in the pipe still and vaporizer, itis, of course, necessary to'maintain a comparatively high temperature in the vaporizer in order to vadesired percentage of the oil passing through the pipe still. AFor example,.if a. gas oil having an average boiling point of 52.5o F. is used as a charging stock and if a vaporizer pressure of only! 50 pounds lwere maintained, it would require a temperature of not much over 700 F. to completely vaporize this oil. If, however, as in the practice of .my process, a substantially higher pressure (say 250 pounds) is maintained in thelv vaporizer, a. temperature of about 8409 F. isfrequired to completely vaporize this o1l. This'is approximate only, and will vary with the nature and the source of the oil. Whatever the pressure may have been, the vapors are in a saturated condition and, therefore, are not in suitable condition to put into the high temperature vapor phase cracking zone. When, however, as in my process, the pressure on` the oil vapors is materially reduced, the vapors are converted into a superheated condition, or, in other words', they are no longer saturated but at a temperature which is above the saturation point for the new pressure existing. This provides a vapor which is thoroughly dried and free of any form of moisture. To accomplish this purpose, the pressure reduction may vary from' 50 to 200 pounds. A suitable condition for operation, under average conditions, is to maintain a pressure of about 250 pounds in the vaporizer and to reduce this ypressure to about 100 pounds on the outlet side of the pressure reducing valve. The entire system may be operated at somewhat lower pressures; for example, the vaporizer may be run at 150 poundsor even less and maybe reduced to 40 to 50 pounds on the outlet side of the pressure reducing valve 7. Maintaining the fractionating equipment at lower pressures still allows suiiicient pressure for passing the dry vapors through the cracking zone atthe required velocities, and the fractionating equipment need be operated' at only slightly above atmospheric pressure.

' The drying of the yoil vapors may also be effected b v combining the process herein described with the introduction of a small percentage of dry gas at about the temperature of the oilvapors into the line between the vaporizer and the cracking coil, as set forth in an4 application, Serial No. 405,870, tiled of even da-tfherewith.

Having now ly described my invention, what I claim and desire to protect by Letters Patent is:

1. The processv of cracking a mineral oil charging stock which comprises vaporizing the oil under-a substantial superatmospheric pressure, drying the oil after it has expanded into vapor by suddenly reducing thepressure thereon not" less than 50 pounds per square inch to the extent required to bring the temperature above the saturation point for the reduced pressure, then heating the oil vapors under the reduced pressure to a cracking temperature and cracking the vaporsmand then cooling and fractionating the vapors.

2. The process of cracking a mineral oil charging stock which comprises heating the ,oil and thereby vaporizing it under a substantial superat-mospheric pressure, allowing the vapors to expand beyond the heating zone and removing heavy fractions, then 5 for the reduced pressure, then heating the oil vapors under the reduced pressure to a cracking temperaturef and cracking the vapors, i and then cooling and fractionating the vapors. y 3. The process of cracking a mineral oil charging stock which comprises heating the oil and Vaporizing it under a pressure of from about 100 to 300 pounds, drying the oil after it has expanded into vapor by suddenly bringing the temperature above the saturation point for the reduced pressure, then heating the oil vapors under the reduced pressure to a cracking temperature and cracking the vapors, and then cooling and fractionating the vapors.

4. The process of cracking a mineral oil charging stock which comprises vaporizing the oil under a pressure of about 15G-300 pounds at a temperature of about 7 .5U-.900 F., suddenly reducing the pressure on the oil after it is expanded into vapor about 100 ounds or less, thereby drying the oil by ringing the temperature above thevsaturation point for the reduced pressure, then l heating -the oil vapors under the reduced pressure to a cracking temperature substan; tially above the temperature at which it Was vaporized, and then cooling and fractionating the vapors. 7

5. The process of cracking a` mineral oil charging stock which comprises flowing the stantial superatmospheric pressure, vheatingl the stock While it is fiowing through said stream to such temperature that substantially allof-it will be in vapor phase in the en'- larged space, then conducting the vapors beyond the enlarged space and suddenly'subf stantially reducing the pressure on the oil vapors not less than 50 pounds per square inch to the extent required to bring the temperature above the saturation point for the reduced pressure, and then heating the oil vapors under such ,reduced pressure to a cracking temperature and crackingI the vapors, and cooling and ractionating the vapors.

6. The process of cracking a mineral oil charging stock which comprises `flowing the stockin an elongated stream of restricted cross-section through a heating zone and then into an enlarged space beyond the heating zone and maintaining the stock under substantial superatmospheric pressure, heating i the stock while' it is flowing through said reducing the pressure thereon about 50 to i 200pounds and thereby drying Ythe oil by stock in an elongated stream of restricted stream to such temperature that substantially all of it will be in vapor phase in the enlarged space, removing from the vapors any entrained; liquid, then conducting the vapors beyond the enlarged space and suddenly substantially reduclng the pressure on the oil vapors, not less than 50 pounds perl square inch to the extent required to bring the temperature above the saturation ,point for the reduced pressure, and then heating the oil vapors under such reduced pressure to a cracking temperature and cracking the vapors, and cooling and fractionating the vapors.

7 The process of cracking a mineral oil charging stock which comprises heating the oil, vaporizing the larger part and separating and removing any unvaporized heavy ends and entrained liquid, conducting said operations under substantial superatmospheric pressure, then drying the oil vapors by suddenly reducing the pressure thereon by an amount not less than 50 pounds per square inch to the extent required to bring the temperature above the saturation point for the reduced pressure, then heating the dried oil vapors under the reduced pressure to a cracking temperature and cracking the vapors, and then cooling and fractionating the vapors..

,In testimony of which invention, I havel hereunto set my hand, at Philadelphia, Pennsylvania, on this 7th day of November, 1929.

ARTHUR E. PEW, JR. 

